The reproduction of documents as images on media sheets generally requires the generation of a source file, the translation of the source file, and the interpretation of the translated file to reproduce an image of the source data. In the first stage, a user generates or edits a source document data file using an application program or imaging device. The source data file may include text, images, and graphics as well as font characteristics, format codes, and the like.
To print the source file onto a substrate, the source data file is translated to a page description format that is implemented with a page description language (PDL), such as PostScript, PDF, PCL, PCL, TIFF, SVG, Metro, or the like. The device-dependent data may be translated to a device-independent color space, such as CIELAB, XYZ, a spot color space such as Pantone, or a profile connection space (PCS). PCS space is defined by one of the profiles that have been developed by the International Color Consortium (ICC). The PDL commands and device-independent color data are provided to a marking or print engine for processing. The print engine decomposes the device-independent data and converts the device-independent color data to the color space of an output device, such as an image output terminal (IOT). The decomposition of the document file includes the interpretation of the PDL commands, which enables the print engine to optimize the imaging of individual objects on a page. The printing device may then be used to generate the raster data that are used to print color images of the document.
Generation of the device-independent data also includes the specification of output parameters for the printing of a job at the printing device. Output parameters that may be selected or adjusted for output of a job include the color, weight, coating, opacity, and white point of the substrate on which a document is reproduced.
Another output parameter that may be defined for a print job is called a rendering intent. Examples of rendering intents include “perceptual,” “saturation,” “absolute calorimetric,” and “relative colorimetric,” all of which are specified by the ICC. Another rendering intent example is “pure.” This rendering intent is specified by the Color Encoding Standard, which is part of the Xerox System Integration Standard published by Xerox Corporation, Palo Alto, Calif., July 1991, XNSS 289107 (hereinafter “The Xerox Color Encoding Standard”). The Xerox Color Encoding Standard describes three reference color systems that attempt to provide device independent color between devices, such as workstations and printers. As is known in the art, each rendering intent specifies an enhancement used for a particular context. For example, “perceptual” makes photographic images more life-like, while “saturation” makes colors brighter and is useful to enhance the look of pie charts, for example. Some output parameters, such as rendering intents, may be specified for different portions or objects of the same page. For example, different rendering intents may be specified for a photographic image, a pie chart, and text that are presented on the same page.
Rendering intents assist the printing device in producing higher quality output. One set of intents may specify a particular halftone that is appropriate for a particular object. For example, a high frequency halftone may be especially appropriate for the edges of text and line art, while a lower frequency halftone may be specified for areas in which the range of color intensities are more important. “Glossmarks” may be implemented by using rendering intents that specify complementary halftones. Also, compression may be used within a real time format that drives a print engine. A rendering intent may be used to identify an appropriate compression for an object, such as lossy compression for JPEG images, for example, or lossless compression, such as flate, LZW, CCITT Group 4 methods for line art and text.
One problem that arises in specifying a rendering intent for objects within a page is the absence of support for the particular output parameter in the program description language used to define the print job. For example, while PostScript and PDF file formats do support color rendering hints, such as “photographic” or “perceptual,” they do not support the specification of other rendering intents, such as halftone selection or compression. Instead, an imager in a printing device interprets the PostScript or PDF file data and infers some of the rendering intents for an object. If a PostScript imager, for example, encounters a PostScript line drawing command, the image may infer that the pixels of the line should be generated with a rendering intent appropriate for either edge or interior line art. Alternatively, the image may analyze the overall intermediate representation of a page and use segmentation algorithms to infer particular rendering intents. This type of analysis evaluates contiguous areas of a representation of a page to determine where edges and images occur, as is well known within the art. In general, therefore, many typically used print job file formats do not support the direct specification of rendering tags for objects within a page.